Polymer/WUCS mat for use in sheet molding compounds

ABSTRACT

A method of forming a molding mat formed bundles of reinforcing fibers and bonding materials is provided. The reinforcing fibers are preferably wet use chopped strand glass fibers (WUCS). The bonding materials may be any thermosetting material having a melting point less than the reinforcing fiber. The molding mat may be formed by partially opening the wet use chopped strand glass fibers and filamentizing the bonding materials, blending the reinforcement and bonding fibers, forming the reinforcement and bonding fibers into a sheet, and bonding the sheet. During bonding, the sheet is heated to a temperature above the melting point of the bonding fibers but below the temperature of the glass fibers. The molding mat thus formed may be used as a reinforcement material in sheet molding compounds.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/024,548 filed Dec. 29, 2004, now U.S. Pat. No. 7,252,729.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates generally to reinforced compositeproducts, and more particularly, to a molding mat that is formed ofbonding materials and bundles of reinforcing fibers and which can beused as a reinforcement material in sheet molding compounds.

BACKGROUND OF THE INVENTION

Glass fibers are useful in a variety of technologies. For example, glassfibers are used as reinforcements in polymer matrices to form glassfiber reinforced plastics or composites. Glass fibers have been used inthe form of continuous or chopped filaments, strands, rovings, wovenfabrics, non-woven fabrics, meshes, and scrims to reinforce polymers.Glass fibers are commonly used as reinforcements in polymer matrices toform glass fiber reinforced plastics or composites because they providedimensional stability as they do not shrink or stretch in response tochanging atmospheric conditions. In addition, glass fibers have hightensile strength, heat resistance, moisture resistance, and high thermalconductivity.

Typically, glass fibers are formed by attenuating streams of a moltenglass material from a bushing or orifice. An aqueous sizing compositioncontaining a film forming polymer, a coupling agent, and a lubricant istypically applied to the fibers after they are drawn from the bushing toprotect the fibers from breakage during subsequent processing and toimprove the compatibility of the fibers with the matrix resins that areto be reinforced. After the sizing composition has been applied, thesized fibers may be gathered into separate strands and wound to producea glass fiber package. The glass fiber package may then be heated toremove water and deposit the size as a residue lightly coating thesurface of the glass fiber. Multiple numbers of the resulting driedglass fiber packages may be consolidated and wound onto a spool referredto as a roving doff or package. The roving package is composed of aglass strand with multiple bundles of glass fibers.

Reinforcement rovings may be used in a sheet molding compound (SMC)process. In an exemplary conventional SMC production process, a layer ofa first resin paste, such as an unsaturated polyester resin or vinylester resin premix, is metered onto a plastic carrier sheet that has anon-adhering surface. Chopped glass fiber roving bundles are thendeposited onto the first layer of resin paste. A second layer of resinpaste is also metered onto a plastic carrier sheet which is then placedon top of the chopped glass/first resin paste layer to form a sandwichmaterial. The first and second layers of resin pastes typically containa mixture of resins and additives such as fillers, pigments, UVstabilizers, catalysts, initiators, inhibitors, mold release agents,and/or thickeners. This sandwiched material may then be compacted todistribute the polymer resin matrix and glass fiber bundles throughoutthe resultant SMC material, which may then be rolled or laid in a boxfor later use in a molding process.

In the production of SMC compounds, it is desirable that the choppedglass fiber bundles contact the polymeric matrix material. One measureof this contact is referred to as wetting, which is a measure of howwell the glass bundles are encapsulated by the matrix SMC resinmaterial. It is desirable to have the glass bundles completely wet withno dry glass. Incomplete wetting during this initial processing canadversely affect subsequent processing of the SMC compound as well asaffect the surface characteristics of the final composite product. Forexample, poor wetting may result in poor molding characteristics of thesheet molding compound, resulting in low composite strengths and surfacedefects in the final composite part. The SMC manufacturing processthroughput, such as lines speeds and productivity, are limited by howwell and how quickly the roving chopped bundles can be completely wet.

Another problem faced by manufacturers of SMC composite products isevenly distributing the chopped glass roving onto the resin paste. If auniform distribution of glass fibers is not provided, the finalcomposite product may possess undesirable properties. Another problemwith conventional SMC processes that use chopped glass roving is thatadding the chopped glass during the manufacturing process is slow andcostly. In addition, loose glass has the potential to be skin irritatingif the fibers come into contact with workers forming the SMC compound.

Therefore, there exists a need in the art for a non-woven mat for use asa reinforcement material in SMC composite products, that improveswetting and correspondingly the SMC production rate and physicalproperties of the composite product, has improved structural and thermalproperties, and is inexpensive to manufacture.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of forminga molding mat that includes of bundles of reinforcing fibers and bondingfibers. In forming the molding mat, bales of wet reinforcing fibers arepartially opened and at least partially dehydrated by removing waterfrom the reinforcement fibers to from dehydrated reinforcement fiberbundles. The reinforcement fiber bundles are mixed with bonding fibersto form a substantially homogenous mixture of reinforcement fiberbundles and bonding fibers. In at least one exemplary embodiment, thebonding fibers are filamentized by an opening apparatus prior to mixingwith the bundles of dehydrated reinforcement fibers. The mixture ofreinforcement fiber bundles and bonding fibers is then formed into asheet, such as by passing the mixture through a sheet former.Optionally, the sheet may be subjected to a needling process tomechanically bond the reinforcement fiber bundles and bonding fibers.The sheet may then be heated to a temperature above the melting point ofthe bonding fibers but below the melting point of the reinforcementfiber bundles to bond the bonding fibers and reinforcing fibers. Abinder resin may be added to the sheet to assist in the bonding of thereinforcement fiber bundles and bonding fibers. The resulting moldingmat may be used as a reinforcement in sheet molding compounds.

It is another object of the present invention to provide a molding matthat may be used as a reinforcement in sheet molding compounds. Themolding mat is formed of a substantially uniform distribution of bundlesof dehydrated wet reinforcement fibers and at least one bondingmaterial. The wet reinforcement fibers may be organic, inorganic, ornatural fibers that provide good structural and thermal properties.Preferably, the wet reinforcement fibers are wet use chopped strandglass fibers. The bonding material has a melting point lower than thereinforcing fibers. Suitable bonding materials include polyester resins,vinyl ester resins, phenolic resins, epoxies, polyamides and styrenes.The molding mat has a weight distribution of from 400-2000 g/m².

It is yet another object of the present invention to provide a method offorming a sheet molding compound material. A first thermosetting resinpaste is deposited onto a first carrier film via a dispensing apparatus.A molding mat formed in accordance with the instant invention is fedfrom a roll and placed on the first resin paste. In at least oneexemplary embodiment, a second thermosetting resin paste is depositedonto a second carrier film and is positioned on the molding mat layersuch that the second thermosetting resin paste is positioned on themolding mat layer. The thus formed sandwiched material is composed ofthe first carrier film, the first thermosetting resin paste, the moldingmat, the second thermosetting resin paste, and the second carrier film.In an alternate embodiment of the present invention, the secondthermosetting resin paste is deposited onto the molding mat layer andthe second carrier film is positioned on the second thermosetting resinpaste. The sandwiched material is then passed through a series of beltsto distribute the first and second thermosetting resin pastes andreinforcement fiber bundles in the molding mat and form a core layercomposed of the mixture of the distributed thermosetting resin pastesand glass fiber bundles. The sheet molding compound (SMC) material thatemerges from the belts may then be wound onto a take-up roll or placedin a box for later use.

It is an advantage of the present invention that the molding mat has auniform or substantially uniform distribution of reinforcement fiberbundles and bonding fibers which provides improved strength, stiffness,impact resistance, and surface qualities.

It is also an advantage of the present invention that the inventivemolding mats have a more uniform weight consistency and uniformproperties compared to conventional chopped strand glass mats.

It is another advantage of the present invention that when wet usechopped strand glass fibers are used as the reinforcing fiber, the glassfibers may be easily opened with little generation of static electricitydue to the moisture present in the glass fibers. In addition, wet usechopped strand glass fibers are less expensive to manufacture than drychopped fibers because dry fibers are typically dried and packaged inseparate steps before being chopped. Therefore, the use of wet usechopped strand glass fibers in forming the molding mat allows SMCcomposite products to be manufactured at lower costs.

The foregoing and other objects, features, and advantages of theinvention will appear more fully hereinafter from a consideration of thedetailed description that follows. It is to be expressly understood,however, that the drawings are for illustrative purposes and are not tobe construed as defining the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of this invention will be apparent upon consideration ofthe following detailed disclosure of the invention, especially whentaken in conjunction with the accompanying drawings wherein:

FIG. 1 is a flow diagram illustrating steps for using wet reinforcementfibers in a dry-laid process according to at least one aspect of thepresent invention;

FIG. 2 is a schematic illustration of an air-laid process using wetreinforcement fibers to form a molding mat according to at least oneexemplary embodiment of the present invention;

FIG. 3 is a schematic illustration of a sheet molding compound processutilizing a molding mat formed from wet use chopped strand glass fibersaccording to at least one exemplary embodiment of the present invention;and

FIG. 4 is a schematic illustration of a matured sheet molding compoundmaterial according to at least one exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are described herein. All references cited herein,including published or corresponding U.S. or foreign patentapplications, issued U.S. or foreign patents, or any other references,are each incorporated by reference in their entireties, including alldata, tables, figures, and text presented in the cited references.

In the drawings, the thickness of the lines, layers, and regions may beexaggerated for clarity. It is to be noted that like numbers foundthroughout the figures denote like elements. The terms “top”, “bottom”,“side”, and the like are used herein for the purpose of explanationonly. It will be understood that when an element such as a layer,region, or other material is referred to as being “on” another element,it can be directly on the other element or intervening elements may bepresent. If an element or layer is described as being “adjacent to” or“against” another element or layer, it is to be appreciated that thatelement or layer may be directly adjacent to or directly against thatother element or layer, or intervening elements may be present. It willalso be understood that when an element or layer is referred to as being“over” another element, it can be directly over the other element, orintervening elements may be present. In addition, the terms “reinforcingfibers” and “reinforcement fibers” may be used interchangeably herein.

The invention relates to a molding mat formed of reinforcing fibers andbonding materials that can be used as a reinforcement in a sheet moldingcompound. The reinforcement fibers may be any type of fibers suitablefor providing good structural qualities as well as good thermalproperties. The reinforcing fibers may be any type of organic,inorganic, or natural fibers. Suitable examples of reinforcing fibersinclude glass fibers, wool glass fibers, natural fibers, metal fibers,ceramic fibers, mineral fibers, carbon fibers, graphite fibers, nylonfibers, rayon fibers, and polymer based thermoplastic materials such as,but not limited to, polyester fibers, polyethylene fibers, polypropylenefibers, polyethylene terephthalate (PET) fibers, polyphenylene sulfide(PPS) fibers, polyvinyl chloride (PVC) fibers, and ethylene vinylacetate/vinyl chloride (EVA/VC) fibers, and mixtures thereof. Themolding mat may be entirely formed of one type of reinforcement fiber(such natural fibers or glass fibers) or, alternatively, more than onetype of reinforcement fiber may be used in forming the molding mat. Theterm “natural fiber” as used in conjunction with the present inventionrefers to plant fibers extracted from any part of a plant, including,but not limited to, the stem, seeds, leaves, roots, or bast. Preferably,the reinforcing fibers are glass fibers.

The reinforcing fibers may be chopped fibers having a discrete length offrom approximately 11-75 mm in length, and preferably, a length of from12-30 mm. Additionally, the reinforcing fibers may have diameters offrom 8-35 microns, and preferably have diameters of from 12-23 microns.Further, the reinforcing fibers may have varying lengths (aspect ratios)and diameters from each other within the molding mat. The reinforcingfibers may be present in the molding mat in an amount of from 80-98% byweight of the total fibers, and are preferably present in the moldingmat in an amount of from 85-95% by weight.

The bonding material may be any thermoplastic or thermosetting materialhaving a melting point less than the reinforcing fibers. Non-limitingexamples of thermoplastic and thermosetting materials suitable for usein the molding mat include polyester fibers, polyethylene fibers,polypropylene fibers, polyethylene terephthalate (PET) fibers,polyphenylene sulfide (PPS) fibers, polyvinyl chloride (PVC) fibers,ethylene vinyl acetate/vinyl chloride (EVA/VC) fibers, lower alkylacrylate polymer fibers, acrylonitrile polymer fibers, partiallyhydrolyzed polyvinyl acetate fibers, polyvinyl alcohol fibers, polyvinylpyrrolidone fibers, styrene acrylate fibers, polyolefins, polyamides,polysulfides, polycarbonates, rayon, nylon, phenolic resins, epoxyresins, and butadiene copolymers such as styrene/butadiene rubber (SBR)and butadiene/acrylonitrile rubber (NBR). It is desirable that one ormore types of thermosetting materials be used to form the molding mat.

In addition, the bonding fibers may be functionalized with acidicgroups, for example, by carboxylating with an acid such as a maleatedacid or an acrylic acid, or the bonding fibers may be functionalized byadding an anhydride group or vinyl acetate. The bonding material mayalso be in the form of a flake, a granule, a resin, or a powder ratherthan in the form of a polymeric fiber.

The bonding material may also be in the form of multicomponent fiberssuch as bicomponent polymer fibers, tricomponent polymer fibers, orplastic-coated mineral fibers such as thermosetting coated glass fibers.The bicomponent fibers may be arranged in a sheath-core, side-by-side,islands-in-the-sea, or segmented-pie arrangement. Preferably, thebicomponent fibers are formed in a sheath-core arrangement in which thesheath is formed of first polymer fibers that substantially surround acore formed of second polymer fibers. It is not required that the sheathfibers totally surround the core fibers. The first polymer fibers have amelting point lower than the melting point of the second polymer fibersso that upon heating the bicomponent fibers to a temperature above themelting point of the first polymer fibers (sheath fibers) and below themelting point of the second polymer fibers (core fibers), the firstpolymer fibers will soften or melt while the second polymer fibersremain intact. This softening of the first polymer fibers (sheathfibers) will cause the first polymer fibers to become sticky and bondthe first polymer fibers to themselves and other fibers that may be inclose proximity.

Numerous combinations of materials can be used to make the bicomponentpolymer fibers, such as, but not limited to, combinations usingpolyester, polypropylene, polysulfide, polyolefin, and polyethylenefibers. Specific polymer combinations for the bicomponent fibers includepolyethylene terephthalate/polypropylene, polyethyleneterephthalate/polyethylene, and polypropylene/polyethylene. Othernon-limiting bicomponent fiber examples include copolyester polyethyleneterephthalate/polyethylene terephthalate (coPET/PET), poly 1,4cyclohexanedimethyl terephthalate/polypropylene (PCT/PP), high densitypolyethylene/polyethylene terephthalate (HDPE/PET), high densitypolyethylene/polypropylene (HDPE/PP), linear low densitypolyethylene/polyethylene terephthalate (LLDPE/PET), nylon 6/nylon 6,6(PA6/PA6,6), and glycol modified polyethylene terephthalate/polyethyleneterephthalate (6PETg/PET).

The bicomponent polymer fibers may have a denier of from about 1-18denier and a length of from 2-4 mm. It is preferred that the firstpolymer fibers (sheath fibers) have a melting point within the range offrom about 150-400° F., and even more preferably in the range of fromabout 170-300° F. The second polymer fibers (core fibers) have a highermelting point, preferably above about 350° F.

The bonding material may be present in the molding mat in an amount offrom 2-20% by weight of the total fibers, and preferably from 2-10% byweight.

The molding mat may be formed by a dry-laid process, such as thedry-laid process described in U.S. patent application Ser. No.10/688,013, filed on Oct. 17, 2003, to Enamul Haque entitled“Development Of Thermoplastic Composites Using Wet Use Chopped StrandGlass In A Dry Laid Process”, which is incorporated by reference in itsentirety. In preferred embodiments, the reinforcing fibers used to formthe molding mat are wet reinforcing fibers, and most preferably are wetuse chopped strand glass fibers. Wet use chopped strand glass fibers foruse as the reinforcement fibers may be formed by conventional processesknown in the art. It is desirable that the wet use chopped strand glassfibers have a moisture content of from 5-30%, and more preferably have amoisture content of from 5-15%.

The use of wet use chopped strand glass fibers provides a cost advantageover conventional dry-laid glass processes. For example, wet use choppedstrand glass fibers are less expensive to manufacture than dry choppedfibers such as dry use chopped strand glass fibers (DUCS) because dryfibers are typically dried and packaged in separate steps before beingchopped. As a result, the use of wet use chopped strand glass fibersallows the molding mat to be manufactured with lower costs.

An exemplary process for forming the molding mat is generallyillustrated in FIG. 1, and includes partially opening the reinforcementfibers and bonding fibers (step 100), blending the reinforcement andbonding fibers (step 110), forming the reinforcement and bonding fibersinto a sheet (step 120), optionally needling the sheet (step 130), andbonding the reinforcement and bonding fibers (step 140).

The reinforcing fibers and the fibers forming the bonding material aretypically agglomerated in the form of a bale of individual fibers. Glassfibers are typically agglomerated in “boxes” of individual fibers. Balesof wet reinforcement fibers (e.g., boxes of wet use chopped strand glassfibers (WUCS)), may be easily opened with little generation of staticelectricity due to the moisture present in the glass fibers. In formingthe molding mat, the bales of wet reinforcing fibers and bonding fibersare at least partially opened by an opening system, such as a baleopening system, common in the industry. The opening system serves todecouple the clustered fibers and enhance fiber-to-fiber contact.

Turning to FIG. 2, the opening of the wet reinforcement fibers and thebonding fibers can best be seen. The wet reinforcing fibers 200 are fedinto a first opening system 220 and the bonding fibers 210 are fed intoa second opening system 230 to at least partially open the wetreinforcing fiber bales and bonding fiber bales respectively. It isdesirable that the first opening system 220 partially open, but notfilamentize, the bales of wet reinforcement fibers 200. It is to benoted that although the exemplary process depicted in FIGS. 1 and 2 showopening the bonding fibers 210 by a second opening system 230, thebonding fibers 210 may be fed directly into the fiber transfer system250 if the bonding fibers 210 are present or obtained in a filamentizedform (not shown), and not present or obtained in the form of a bale offibers. Such an embodiment is considered to be within the purview ofthis invention.

The first and second opening systems 220, 230 are preferably baleopeners, but may be any type of opener suitable for opening the bales ofbonding fibers 210 and bales of wet reinforcing fibers 200. The designof the openers depends on the type and physical characteristics of thefiber being opened. Suitable openers for use in the present inventioninclude any conventional standard type bale openers with or without aweighing device. The weighing device serves to continuously weigh thepartially opened fibers as they are passed through the bale opener tomonitor the amount of fibers that are passed onto the next processingstep. The bale openers may be equipped with various fine openers, one ormore licker-in drums or saw-tooth drums, feeding rollers, and/or or acombination of a feeding roller and a nose bar.

In alternate embodiments where the bonding material is in the form of aflake, granule, or powder (not shown), and not a bonding fiber, thesecond opening system 230 may be replaced with an apparatus suitable fordistributing the powdered, flaked, or granule bonding material to thefiber transfer system 250 for mixing with the reinforcement fibers 200.A suitable apparatus would be easily identified by those of skill in theart. In embodiments where a resin in the form of a flake, granule, orpowder is used in addition to the bonding fibers 210 (not shown), theapparatus for distributing the flakes, granules, or powder typicallydoes not replace the second opening system 230. The flakes, granules, orpowder may be fed directly into the fiber transfer system 250 for mixingwith the reinforcement fiber bundles and bonding material.

The partially opened bales of wet reinforcement fibers 200(reinforcement fiber bundles) may then be dosed or fed from the firstopening system 220 to a condensing unit 240 to remove water from the wetfibers. In exemplary embodiments, greater than 70% of the free water(water that is external to the reinforcement fibers) is removed.Preferably, however, substantially all of the water is removed by thecondensing unit 240. It should be noted that the phrase “substantiallyall of the water” as it is used herein is meant to denote that all ornearly all of the free water is removed. The condensing unit 240 may beany known drying or water removal device known in the art, such as, butnot limited to, an air dryer, an oven, rollers, a suction pump, a heateddrum dryer, an infrared heating source, a hot air blower, or a microwaveemitting source.

The bundles of reinforcing fibers 200 and the bonding fibers 210 areblended together by the fiber transfer system 250. In preferredembodiments, the fibers are blended in a high velocity air stream. Thefiber transfer system 250 serves both as a conduit to transport thebonding fibers 210 and bundles of reinforcing fibers 200 to the sheetformer 270 and to substantially uniformly mix the fibers in the airstream. It is desirable to distribute the reinforcing fiber bundles 200and bonding fibers 210 as uniformly as possible. The ratio ofreinforcing fibers 200 and bonding fibers 210 entering the air stream inthe fiber transfer system 250 may be controlled by weighing device suchas described above with respect to the first and second opening systems220, 230 or by the amount and/or speed at which the fibers are passedthrough the first and second opening systems 220, 230. In preferredembodiments, the ratio of reinforcing fibers 200 to bonding fibers 210present in the air stream is 90:10, reinforcement fibers 200 to bondingfibers 210 respectively.

The mixture of reinforcing fibers 200 and bonding fibers 210 may betransferred by the air stream in the fiber transfer system 250 to asheet former 270 where the fibers are formed into a sheet. One or moresheet formers may be utilized in forming the molding mat. In someembodiments of the present invention, the blended fibers are transportedby the fiber transfer system 250 to a filling box tower 260 where thebundles of reinforcing fibers 200 and bonding fibers 210 arevolumetrically fed into the sheet former 270, such as by a computermonitored electronic weighing apparatus, prior to entering the sheetformer 270. The filling box tower 260 may be located internally in thesheet former 270 or it may be positioned external to the sheet former270. The filling box tower 260 may also include baffles to further blendand mix the reinforcement fiber bundles 200 and bonding fibers 210 priorto entering the sheet former 270. In some embodiments, a sheet former270 having a condenser and a distribution conveyor may be used toachieve a higher fiber feed into the filling box tower 260 and anincreased volume of air through the filling box tower 260. In order toachieve an improved cross-distribution of the opened fibers, thedistributor conveyor may run transversally to the direction of thesheet. As a result, the bonding fibers 210 and the bundles ofreinforcing fibers 200 may be transferred into the filling box tower 260with little or no pressure and minimal fiber breakage.

The sheet formed by the sheet former 270 contains a uniform orsubstantially uniform distribution of bundles of reinforcing fibers 200and bonding fibers 210 at a desired ratio and weight distribution. Inparticular, the sheet formed by the sheet former 270 may have a weightdistribution of from 400-2000 g/m², with a preferred weight distributionof from about 400-1000 g/m².

In one or more embodiments of the invention, the sheet exiting the sheetformer 270 is subjected to a needling process in a needle feltingapparatus 280 in which barbed or forked needles are pushed in a downwardand/or upward motion through the fibers of the sheet to entangle orintertwine the reinforcing fibers 200 and bonding fibers 210 and impartmechanical strength and integrity to the mat. The needle feltingapparatus 280 may include a web feeding mechanism, a needle beam with aneedleboard, barbed felting needles ranging in number from about 500 permeter to about 7,500 per meter of machine width, a stripper plate, a bedplate, and a take-up mechanism. Mechanical interlocking of thereinforcement fibers 200 and bonding fibers 210 is achieved by passingthe barbed felting needles repeatedly into and out of the sheet. Anoptimal needle selection for use with the particular reinforcement fiberand polymer fiber chosen for use in the inventive process would beeasily identified by one of skill in the art.

Although the bonding fibers 210 are used to bond the reinforcing fibers200 to each other, a binder resin 285 may be added as a bonding agentprior to passing the sheet through the thermal bonding system 290. Thebinder resin 285 may be in the form of a resin powder, flake, granule,foam, or liquid spray. The binder resin 285 may be added by any suitablemanner, such as, for example, a flood and extract method or by sprayingthe binder resin 285 on the sheet. The amount of binder resin 285 addedto the sheet may be varied depending of the desired characteristics ofthe molding mat. A catalyst such as ammonium chloride, p-toluene,sulfonic acid, aluminum sulfate, ammonium phosphate, or zinc nitrate maybe used to improve the rate of curing and the quality of the curedbinder resin 285.

Another process that may be employed to further bond the reinforcingfibers 200 either alone, or in addition to, the other bonding methodsdescribed herein, is latex bonding. In latex bonding, polymers formedfrom monomers such as ethylene (T_(g) −125° C.), butadiene (T_(g) −78°C.), butyl acrylate (T_(g) −52° C.), ethyl acrylate (T_(g) −22° C.),vinyl acetate (T_(g) 30° C.), vinyl chloride (T_(g) 80° C.), methylmethacrylate (T_(g) 105° C.), styrene (T_(g) 105 C.°), and acrylonitrile(T_(g) 130° C.) are used as bonding agents. A lower glass transitiontemperature (T_(g)) results in a softer polymer. Latex polymers may beadded as a spray prior to the sheet entering the thermal bonding system290. Once the sheet enters the thermal bonding system 290, the latexpolymers melt and bond the reinforcement fibers 200 together.

A further optional bonding process that may be used alone, or incombination with the other bonding processes described herein ischemical bonding. Liquid based bonding agents, powdered adhesives,foams, and, in some instances, organic solvents can be used as thechemical bonding agent. Suitable examples of chemical bonding agentsinclude, but are not limited to, acrylate polymers and copolymers,styrene-butadiene copolymers, vinyl acetate ethylene copolymers, andcombinations thereof. For example, polyvinyl acetate (PVA), ethylenevinyl acetate/vinyl chloride (EVA/VC), lower alkyl acrylate polymer,styrene-butadiene rubber, acrylonitrile polymer, polyurethane, epoxyresins, polyvinyl chloride, polyvinylidene chloride, and copolymers ofvinylidene chloride with other monomers, partially hydrolyzed polyvinylacetate, polyvinyl alcohol, polyvinyl pyrrolidone, polyester resins,vinyl ester resins, phenolic resins, and styrene acrylate may be used asa chemical bonding agent. The chemical bonding agent may be applieduniformly by impregnating, coating, or spraying the sheet.

Either after the sheet exits the sheet former 270 or after the optionalneedling of the sheet, the sheet may be passed through a thermal bondingsystem 290 to bond the reinforcement fibers 200 and bonding fibers 210and form the molding mat 295. However, it is to be appreciated that ifthe sheet is needled in the needle felting apparatus 280 and thereinforcing fibers 200 and the bonding fibers 210 are mechanicallybonded, the sheet may not need to be passed through the thermal bondingsystem 290 to form the molding mat 295.

In the thermal bonding system 290, the sheet is heated to a temperaturethat is above the melting point of the bonding fibers 210 but below themelting point of the reinforcement fibers 200. When bicomponent fibersare used as the bonding fibers 210, the temperature in the thermalbonding system 290 is raised to a temperature that is above the meltingtemperature of the sheath fibers, but below the melting temperature ofthe reinforcement fibers 200. Heating the bonding fibers 210 to atemperature above their melting point(s), or the melting point of thesheath fibers in the instance where the bonding fibers 210 arebicomponent fibers, causes the bonding fibers 210 to become adhesive andbond the bonding fibers 210 both to themselves and to the reinforcingfibers 200. The melted bonding fibers 210 act as a glue to hold thedispersed glass fibers in bundles. If the bonding fibers 210 completelymelt, the melted fibers may encapsulate the reinforcement fibers 200. Aslong as the temperature within the thermal bonding system 290 is notraised as high as the melting point of the reinforcing fibers and/orcore fibers, these fibers will remain in a fibrous form within thethermal bonding system 290 and molding mat 295.

The thermal bonding system 290 may include any known heating and/orbonding method known in the art, such as oven bonding, oven bondingusing forced air, infrared heating, hot calendaring, belt calendaring,ultrasonic bonding, microwave heating, and heated drums. Optionally, twoor more of these bonding methods may be used in combination to bond thereinforcing fibers 200 and bonding fibers 210. The temperature of thethermal bonding system 290 varies depending on the melting point of theparticular bonding fibers 210, binder resins, and/or latex polymersused, and whether or not bicomponent fibers are present in the sheet.The molding mat 295 that emerges from the thermal bonding system 290contains dispersed bonding fibers and reinforcement fibers in bundles.When wet use chopped strand glass is used as the wet reinforcing fibers200, the molding mat 295 that emerges from the thermal bonding system290 contains uniformly or nearly uniformly dispersed bonding fibers 210and glass filaments in bundles. The uniform or nearly uniformdistribution of reinforcement fiber bundles 200 and bonding fibers 210in the molding mat 295 provides improved strength, improved thermalproperties, improved stiffness, and improved impact resistance to thefinal composite product. In addition, the molding mat 295 has a moreuniform weight consistency compared to conventional chopped strand glassmats. Uniform weight consistency in the inventive molding mats resultsin uniform properties such as flexural and impact strength in the finalproducts. In the molding mat of the present invention, the glass contentvariability is approximately +/−1.5% and the weight consistency isapproximately +/−5%. Further, the uniform properties of the inventivemolding mat permits the use of lower weight reinforcements thantraditional chopped strand glass mats.

The molding mat 295 provides the ability to optimize and/or tailor thephysical properties (such as stiffness or strength) needed for specificapplications by altering the weight, length, and/or diameter of thereinforcement fibers and/or bonding fibers used in forming the moldingmat. In addition, the sizing chemistry of the reinforcement fibers maybe easily adapted to match the properties of individual types of bondingfibers. As a result, a large variety of molding mats and compositeproducts formed using the molding mats, such as products formed fromsheet molding compounds, can be made.

In an alternate embodiment (not illustrated), the molding mat is formedby a wet-laid process. For example, reinforcing fibers and bondingfibers are dispersed in an aqueous solution that contains a binder aswell as dispersants, viscosity modifiers, defoaming agents, and/or otherchemical agents and agitated to form a slurry. The bonding fibers andreinforcing fibers located in the slurry are then deposited onto amoving screen where water is removed. Optionally, the mat is dried in anoven. The mat may then be immersed in a binder composition to impregnatethe mat with the binder composition. The mat is then passed through acuring oven to remove any remaining water, cure the binder, and at leastpartially melt the bonding fibers to bind the reinforcing fibers andbonding fibers together. The resulting molding mat is an assembly ofdispersed bonding fibers and glass filaments in bundles.

In at least one exemplary embodiment of the invention, the molding mat295 is utilized in a sheet molding compound (SMC) process. One exampleof a sheet molding compound process that incorporates the molding mat ofthe present invention is illustrated in FIG. 3. A first carrier film 310is fed from a first carrier roll 320 onto a moving conveyor belt 300. Afirst thermosetting resin paste 315 is applied to the first carrier film310 via a dispensing apparatus 325. A molding mat 295 formed inaccordance with the present invention is then fed from a roll 330 ontothe first thermosetting resin paste 315 on the first carrier film 310. Asecond thermosetting resin paste 335 is deposited onto a second carrierfilm 340 fed from a second carrier roll 345 and is positioned on themolding mat layer 350 such that the second thermosetting resin paste 335on the second carrier film 340 contacts the molding mat layer 350 andforms a sandwiched material that includes the first carrier film 310,the first thermosetting resin paste 315, the molding mat 295, the secondthermosetting resin paste 335, and the second carrier film 340. In analternative embodiment (not shown), the second thermosetting resin paste335 may be deposited onto the molding mat layer 350 and the secondcarrier film 340 may be positioned on the second thermosetting resinpaste 335.

The first and second thermosetting resin pastes, 315, 335 may be formedby mixing one or more suitable thermosetting materials, such aspolyester resins, vinyl ester resins, phenolic resins, epoxies,polyimides, and/or styrenes, and any desired additives such as fillers,pigments, UV stabilizers, catalysts, initiators, inhibitors, moldrelease agents, thickeners, and the like. It is preferred that a fillerbe mixed with the thermosetting material in forming the thermosettingresin pastes 315, 335. Suitable examples of fillers include calciumcarbonate, alumina trihydrate, mica, talc, glass bubbles, andwoolastonite. However, adding a filler to the dispensing apparatus 325along with the first and second thermosetting resin pastes 315, 335 isalso considered to be within the purview of the invention. The first andsecond thermosetting resin pastes 315, 335 can be made at the same timein a mixing tank. It is also preferred that the thermosetting resinpastes 315, 335 include a thickening agent such as magnesium oxide,magnesium hydroxide, and/or calcium oxide. The thickener (or thickeningagent paste) is added to the thermosetting resin pastes immediately, ornearly immediately, prior to transporting the thermosetting resin pastes315, 335 to the dispensing apparatuses. The first and secondthermosetting resin pastes 315, 335 may be compounded using the sameresins. Non-limiting examples of materials used for the first and secondcarrier films 310, 340 include polymeric films such as polyethylene andnylon.

The sandwiched material is then passed through a series of belts 360,370 where the sandwiched material is compacted to distribute the firstand second thermosetting resin pastes 315, 335 and reinforcement fiberbundles in the molding mat 295 and form an intermediate layer 395 formedof the mixture of the distributed thermosetting resin pastes 315, 335 inthe molding mat 295. The belts are preferably wire mesh belts to improvewet out of the reinforcement fibers by the first and second resin pastes315, 335. Because the reinforcement fibers in the molding mat 295 arenot filamentized and are present as bundles of fibers, they have theability to wet with the thermosetting resin pastes and fillers in thesandwiched material. If the reinforcing fibers do not wet the bondingcomponent(s) of the sheet molding compound, there may be poor mechanicalperformance of the final composite product and/or reduced porosity inthe composite product. The resultant sheet molding compound (SMC)material 380 that emerges from the belts 360, 370 may then be wound ontoa take up roll 390 as illustrated in FIG. 3 or placed in boxes (notshown) for later use.

The SMC material 380 may then be stored at a substantially constanttemperature for 2-5 days to mature. During this maturation time, the SMCmaterial 290 increases in viscosity to approximately 15-40 millioncentipoise. As the viscosity increases, the first and second resinpastes and the glass fiber bundles in the molding mat in theintermediate layer form an integral composite layer. A schematicdepiction of the matured SMC material may be seen in FIG. 4. Inparticular, the matured SMC material 400 includes an integral compositelayer 405 sandwiched between the first carrier film 310 and the secondcarrier film 340.

The matured SMC material 400 may be molded in a subsequent moldingprocess to form the final composite product. For example, the maturedSMC material 400 can be used in a matched die molding process (notillustrated). In this molding process, the first and second carrierfilms 310,340 are removed from the matured SMC material 400 and thematured SMC material 400 is cut into pieces having a pre-determined size(charge). Pieces of the matured SMC material 400 are placed into a moldhaving a female and a male half, the halves of the mold are closed, andheat and pressure are applied to compress the charge, cure thethermosetting resins, and form the matured SMC material 400 into thepre-determined shape.

Once the molding cycle is complete, the mold is opened and the compositeproduct is removed. The pressure within the mold may range from 200-1500psi, preferably from 200-1200 psi, and the temperature within the moldmay range from 100-170° C., preferably from 140-160° C. The moldingcycle for the SMC material may be from 0.5-3.0 minutes, depending on thespecific thermosetting resin used and the thickness of the finalcomposite part. In addition to matched metal die molding (compressionmolding), the matured SMC material 400 may also be used in vacuum andpressure bagging, cold press molding, injection molding, and centrifugalcasting to form composite products It should be appreciated thatalthough the above-described process for forming the sheet moldingmaterial and molding it into a composite product has been described inwhat is believed to be the preferred embodiment, other variations andalternatives to the process identifiable to those of skill in the artare also considered to be within the purview of the invention.

The molding mat 295 provides improved flow and conformability of the SMCmaterial 380 to the shape of the mold. Also, molding mats according tothe instant invention provide improved molding capability by increasingthe draw ratio and are thus able to conform to the shape of the mold andprovide uniform properties to the composite product.

The SMC material 380 may be used to form a variety of composite productsin numerous applications, such as in automotive applications includingthe formation of door panels, trim panels, exterior body panels, loadfloors, bumper, front ends, underbody shields, running boards,sunshades, instrument panel structures, door inners, etc. The SMCmaterial 380 is particularly advantageous in automotive applicationsbecause the sheet molding compound material 380 offers a weightreduction in the formed composite part, corrosion resistance to theformed part, resistance to minor impacts, part consolidation, andimproved surface quality, especially when compared to steel formedparts. Because the molding mat 295 of the present invention includespolymer fibers, the SMC material 380 has the advantage of improvedelongation characteristics and reduced micro-cracking in the compositepart. The use of polymer fibers having high elongation characteristics,such as polyethylene terephthalate (PET) fibers, further reduces thegeneration of micro-cracks in the composite parts formed from the SMCmaterial 380. Further advantages of the SMC material 380 include ashorter tooling lead time and lower tooling cost to form the product.Other applications for the SMC material 380 include furnitureapplications (chairs, tabletops, etc.), household appliances (washingmachine doors, refrigerator housings, etc.), business machines (computerhousings), jet ski bodies, office screens and partitions, ceiling tiles,building panels, satellite dishes, electrical boxes, and man-holecovers.

The invention of this application has been described above bothgenerically and with regard to specific embodiments. Although theinvention has been set forth in what is believed to be the preferredembodiments, a wide variety of alternatives known to those of skill inthe art can be selected within the generic disclosure. The invention isnot otherwise limited, except for the recitation of the claims set forthbelow.

1. A method of forming a sheet molding compound material, the methodcomprising: depositing a first thermosetting resin paste onto a firstcarrier film; forming a molding mat; placing said molding mat on saidfirst thermosetting resin paste, said molding mat including dehydratedreinforcement fiber bundles and a bonding material having a meltingpoint less than the melting point of said dehydrated reinforcement fiberbundles; depositing a second thermosetting resin paste onto a secondcarrier film; positioning said second carrier film containing saidsecond thermosetting resin paste such that said second thermosettingresin paste is positioned on said molding mat to form a sandwichedmaterial; and compacting said sandwiched material to form said sheetmolding compound material, wherein said molding mat is formed by: atleast partially opening bales of wet reinforcement fibers; removingwater from said at least partially opened bales of wet reinforcementfibers to form said dehydrated reinforcement fiber bundles; mixing saiddehydrated reinforcement fiber bundles with said bonding material toform a substantially uniform mixture of said dehydrated reinforcementfiber bundles and said bonding material; forming said mixture ofdehydrated reinforcement fiber bundles and said bonding material into asheet; and bonding said dehydrated reinforcement fiber bundles and saidbonding material to form said molding mat.
 2. The method of claim 1,wherein said wet reinforcement fibers are wet use chopped strand glassfibers.
 3. The method of claim 1, wherein said compacting step includes:passing said sandwiched material through a series of belts to distributesaid first and second thermosetting resin pastes and said dehydratedreinforcement fiber bundles.
 4. A method of making a molded sheetmolding composite product, the method comprising: depositing a firstthermosetting resin paste onto a first carrier film; placing a moldingmat on said first thermosetting resin paste, said molding mat includingdehydrated reinforcement fiber bundles and-bonding fibers having amelting point less than the melting point of said dehydratedreinforcement fiber bundles; depositing a second thermosetting resinpaste onto a second carrier film; positioning said second carrier filmcontaining said second thermosetting resin paste such that said secondthemiosetting resin paste is positioned on said molding mat to form asandwiched material; compacting said sandwiched material to form a sheetmolding compound material; storing said sheet molding compound materialto form a matured sheet molding compound; and molding said matured sheetmolding compound to form a molded sheet molding composite product,wherein said molded mat is formed by: at least partially opening balesof wet reinforcement fibers; removing water from said at least partiallyopened bales of wet reinforcement fibers to form said dehydratedreinforcement fiber bundles; mixing said dehydrated reinforcement fiberbundles with said bonding fibers to form a substantially uniform mixtureof said dehydrated reinforcement fiber bundles and said bonding fibers;forming said mixture of dehydrated reinforcement fiber bundles and saidbonding fibers into a sheet; and bonding said dehydrated reinforcementfiber bundles and said bonding fibers to form said molding mat.
 5. Themethod of claim 4, wherein said wet reinforcement fibers are wet usechopped strand glass fibers.
 6. The method of claim 5, wherein saidbonding step comprises: heating said sheet to a temperature above themelting point of said bonding fibers and below the melting point of saiddehydrated reinforcement fiber bundles to at least partially melt saidbonding fibers and bond at least a portion of said dehydratedreinforcement fiber bundles and said bonding fibers.
 7. The method ofclaim 4, further comprising the steps of: removing said first and secondcarrier films prior to said molding step; and cutting said matured sheetmolding compound into pieces having a predetermined size.
 8. The methodof claim 4, further comprising the steps of: admixing a firstthermosetting material, a filler, and additives to form said firstthermosetting resin paste; and transporting said first thermosettingresin paste to a dispensing apparatus prior to depositing said firstthermosetting resin paste onto said first carrier film, said additivesbeing selected from the group consisting of pigments, UV stabilizers,catalysts, initiators, inhibitors, mold release agents, thickeners andcombinations thereof.
 9. The method of claim 8, further comprising thesteps of: admixing a second thermosetting material, a filler, andadditives to form said second thermosetting resin paste; andtransporting said second thermosetting resin paste to a seconddispensing apparatus prior to depositing said second thermosetting resinpaste onto said second carrier film, said additives being selected fromthe group consisting of pigments, UV stabilizers, catalysts, initiators,inhibitors, thickeners and combinations thereof.
 10. The method of claim4, wherein said compacting step includes: passing said sandwichedmaterial through a series of belts to distribute said first and secondthermosetting resin pastes and said dehydrated reinforcement fiberbundles.